CN118738261A - Positive electrode sheet and preparation method thereof, electrode assembly, battery cell, battery and electrical device - Google Patents

Abstract

The present invention relates to the field of battery technology, and in particular to a positive electrode plate and a preparation method thereof, an electrode assembly, a battery cell, a battery and an electrical device. The positive electrode plate includes a current collector and a coating provided on at least one side of the current collector, and a protective film is provided on the surface of the coating, and the material of the protective film includes fluoride. Considering that the positive electrode material in the coating will lead to performance degradation when it contacts with air, and that the positive electrode material will have an interfacial side reaction when it contacts with an electrolyte, in order to improve the performance of the positive electrode material, a protective film is provided on the surface of the coating to reduce the chance of the positive electrode material contacting with air, and reduce the probability of the positive electrode material having an interfacial reaction with the electrolyte, thereby improving the stability of the positive electrode material and improving the performance of the battery.

Description

Positive electrode sheet and preparation method thereof, electrode assembly, battery cell, battery and power-using device

Technical Field

The present invention relates to the technical field of batteries, and in particular to a positive electrode sheet and a preparation method thereof, an electrode assembly, a battery cell, a battery and an electrical device.

Background Art

Lithium-ion batteries have become the most popular energy storage system due to their high operating potential, long life and environmental friendliness. They are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids and other fields.

There is a problem of battery performance deterioration during the cycle of lithium-ion batteries.

Summary of the invention

The main purpose of the present invention is to provide a positive electrode plate, aiming to improve the performance of the battery.

To achieve the above object, the present invention provides a positive electrode plate, which includes a current collector and a coating provided on at least one side of the current collector, a surface of the coating is provided with a protective film, and the material of the protective film includes fluoride.

The positive electrode sheet of the present application includes a current collector and a coating disposed on at least one side of the current collector, and a protective film is disposed on the surface of the coating, and the material of the protective film includes fluoride. Considering that the positive electrode material in the coating will lead to performance degradation when it contacts the air, and that the positive electrode material will have an interface side reaction when it contacts the electrolyte, in order to improve the performance of the positive electrode material, a protective film is disposed on the surface of the coating to reduce the chance of the positive electrode material contacting the air, and reduce the probability of the positive electrode material and the electrolyte having an interface reaction, thereby improving the stability of the positive electrode material and improving the performance of the battery.

Optionally, the protective film has a thickness ranging from 1 nm to 50 nm, preferably from 5 nm to 20 nm.

In order to make the protective film effectively reduce the chance of contact between the electrolyte and the coating and ensure that the lithium ions have a good migration rate, the thickness of the protective film ranges from 1 nm to 50 nm, preferably from 5 nm to 20 nm.

Optionally, the fluoride includes at least one of lithium fluoride and aluminum fluoride.

The fluoride includes at least one of lithium fluoride and aluminum fluoride. That is, the protective film may include lithium fluoride and aluminum fluoride at the same time, or may be independently composed of lithium fluoride or aluminum fluoride. Of course, in some cases, other types of materials may be added to the protective film as needed, which is not limited in this application and can be designed according to usage requirements.

Optionally, the protective film includes a lithium fluoride protective film and an aluminum fluoride protective film, and the lithium fluoride protective film and the aluminum fluoride protective film are stacked on the surface of the coating;

And/or, the protective film includes a lithium fluoride protective film and an aluminum fluoride protective film, at least a portion of the surface of the coating is provided with the lithium fluoride protective film, and at least another portion of the surface of the coating is provided with the aluminum fluoride protective film.

The lithium fluoride protective film and the aluminum fluoride protective film are stacked on the surface of the coating, and the lithium fluoride protective film 30a and the aluminum fluoride protective film 30b are alternately arranged on the surface of the coating 20. For example, the lithium fluoride protective film 30a is arranged on the surface of the coating 20, and the aluminum fluoride protective film 30b is arranged on the side of the lithium fluoride protective film 30a away from the coating 20. Of course, the aluminum fluoride protective film 30b can also be arranged on the surface of the coating 20, and the lithium fluoride protective film 30a is arranged on the side of the aluminum fluoride protective film 30b away from the coating 20. The number of layers of the lithium fluoride protective film 30a and the aluminum fluoride protective film 30b is not specifically limited. For example, the lithium fluoride protective film 30a has two layers, and the aluminum fluoride protective film 30b has one layer. The aluminum fluoride protective film 30b is arranged between the two layers of lithium fluoride protective film 30a, which can be arranged according to needs.

At least a portion of the surface of the coating is provided with a lithium fluoride protective film, and at least another portion of the surface of the coating is provided with an aluminum fluoride protective film. The lithium fluoride protective film 30a is provided on at least a portion of the surface of the coating 20, and the aluminum fluoride protective film 30b is provided on at least another portion of the surface of the coating 20. It can be understood that the lithium fluoride protective film 30a and the aluminum fluoride protective film 30b can be arranged side by side on one surface of the coating 20 without any specific limitation, and can be considered as needed.

Optionally, the coating layer includes a positive electrode material, a coating layer is formed on the surface of the positive electrode material, and the coating layer includes at least one of a sulfur-containing compound, a boron-containing compound, and a fluoride.

Positive electrode materials, for example, ternary positive electrode materials, especially the higher the nickel content, the higher the residual lithium compounds on the surface during the synthesis process. Such surface residual lithium can easily absorb carbon dioxide and water in the air, forming _Li2CO3 and LiOH _layers on the particle surface, which will have the following effects: it consumes the Li in the material and has no electrochemical activity, thus causing capacity decay; LiOH will react with polyvinylidene fluoride PVDF to cause gelation of the slurry, and the LiOH remaining on the electrode may also react with the electrolyte _LiPF6 to consume the Li ions in the electrolyte and produce HF, which will further corrode the positive electrode material and alienate its surface; the dense _Li2CO3 layer on the surface of the positive electrode particles will also hinder the diffusion of Li in the _future , affecting the battery's electrical performance.

In order to solve the above problems, the residual lithium compounds are reduced or eliminated through chemical reactions, and an ion-conductive coating layer is formed on the surface of the positive electrode material to reduce battery polarization. The coating layer includes at least one of sulfur-containing compounds, boron-containing compounds, and fluorides.

Optionally, the coating layer is lithium fluoride.

The coating layer is lithium fluoride obtained by reacting ammonium fluoride. The residual lithium can be completely removed by controlling the amount of ammonium fluoride added to the reaction. And controlling the operation steps can effectively remove the reaction byproducts, thus avoiding the introduction of new impurities.

Furthermore, the step of adding ammonium fluoride can be performed during the process of preparing the coating slurry without adding additional steps, thereby improving the preparation efficiency of the positive electrode sheet.

Optionally, the mass percentage of the lithium fluoride to the total mass of the positive electrode material is 0.01% to 5%, preferably 0.5% to 1.2%.

In the process of obtaining a lithium fluoride coating layer by reacting residual lithium with ammonium fluoride, the amount of ammonium fluoride to be added can be converted according to the amount of residual lithium in the positive electrode material to completely react the residual lithium. In the obtained positive electrode material, the mass percentage of lithium fluoride to the total mass of the positive electrode material is 0.01% to 5%, preferably 0.5% to 1.2%.

Optionally, the general formula of the positive electrode material in the coating is Li _x Ni _y M _1-y O ₂ , 0.9≤x≤1.15, 0.6≤y≤1, and M is selected from one or more of Co, Mn, and Al;

And/or, the general formula of the positive electrode material in the coating is xLi ₂ MnO ₃ .(1-x)LiMO ₂ , 0.1≤x≤0.9, and M is selected from one or more of Co, Mn, and Al.

The positive electrode material in the coating includes Li _x Ni _y M _1-y O ₂ with a layered structure, 0.9≤x≤1.15, 0.6≤y≤1, M is selected from one or more of Co, Mn, and Al, and/or includes lithium-rich manganese-based positive electrode material xLi ₂ MnO ₃ .(1-x)LiMO ₂ , 0.1≤x≤0.9, M is selected from one or more of Co, Mn, and Al.

The present application also provides a method for preparing a positive electrode sheet, comprising:

Prepare the positive electrode;

preparing fluoride precursors;

A protective film is formed on the coating surface of the positive electrode plate by thin film deposition technology.

In order to form a protective film on the coating surface of the positive electrode plate, the steps include preparing the positive electrode plate, preparing a fluoride precursor, and forming a protective film on the coating surface of the positive electrode plate by thin film deposition technology.

It is understandable that thin film deposition technology includes chemical vapor deposition and physical vapor deposition. The present application does not limit which deposition technology is used to form a protective film on the coating surface, and the selection can be made according to the experimental environment and actual needs.

Optionally, the thin film deposition technology includes an atomic layer deposition process.

Thin film deposition technologies include chemical vapor deposition and physical vapor deposition. There is no limitation on the specific process to be selected. In order to make the prepared protective film have better effect, the atomic layer deposition process is preferably selected. The atomic deposition process has better chemical ratio, strong stress control ability, smooth film surface, wide process window range, and wider range of precursor selection.

Optionally, the fluoride comprises lithium fluoride and/or aluminum fluoride.

Fluoride can effectively reduce the oxidation activity of the positive electrode material surface, inhibit the oxidative decomposition of the electrolyte at the positive electrode, and promote the lithium ion transport in the solid phase. A fluoride protective film is formed on the coating surface of the positive electrode plate by preparing a fluoride precursor and using a thin film deposition technique. The fluoride precursor includes a lithium fluoride precursor and/or an aluminum fluoride precursor.

Optionally, the step of forming a coating layer on the coating surface of the positive electrode plate by an atomic layer deposition process includes:

The positive electrode sheet is placed in an atomic layer deposition reaction chamber, vacuumed, and the deposition temperature is set to 200° C.-250° C.;

A suitable fluoride precursor is introduced into the reaction chamber to form a protective film on the surface of the coating, and the vacuum is opened to remove the unreacted precursor. The above steps are repeated to obtain a protective film of a preset thickness.

The material of the protective film includes fluoride, and the type of fluoride is not specifically limited. The precursor can be selected according to the selected fluoride type. In the step of forming a coating layer on the coating surface of the positive electrode plate through an atomic layer deposition process, the process includes: placing the positive electrode plate into an atomic layer deposition reaction chamber, evacuating the chamber, and setting the deposition temperature to 200°C-250°C; introducing a suitable fluoride precursor into the reaction chamber to form a protective film on the surface of the coating, opening the vacuum to remove unreacted precursors, and repeating the above steps to obtain a protective film of a preset thickness.

Optionally, the step of introducing a suitable fluoride precursor into the reaction chamber to form a protective film on the surface of the coating, opening the vacuum to remove the unreacted precursor, and repeating the above steps to obtain a protective film of a preset thickness includes:

A precursor of aluminum fluoride is introduced into the reaction chamber to form a protective film on the surface of the coating, and the vacuum is opened to remove the unreacted precursor;

A lithium fluoride precursor is introduced into the reaction chamber to form a protective film on the surface of the coating, and the vacuum is opened to remove the unreacted precursor;

Repeat the above steps to obtain a protective film of a preset thickness.

The fluoride includes at least one of lithium fluoride and aluminum fluoride. In order to obtain a protective film of lithium fluoride and aluminum fluoride, a suitable fluoride precursor is introduced into the reaction chamber to form a protective film on the surface of the coating, the vacuum is opened to remove the unreacted precursor, and the above steps are repeated to obtain a protective film of a preset thickness, including: introducing an aluminum fluoride precursor into the reaction chamber to form a protective film on the surface of the coating, opening the vacuum to remove the unreacted precursor; introducing a lithium fluoride precursor into the reaction chamber to form a protective film on the surface of the coating, opening the vacuum to remove the unreacted precursor; repeating the above steps to obtain a protective film of a preset thickness.

Optionally, the step of introducing an aluminum fluoride precursor into the reaction chamber to form a protective film on the surface of the coating and opening the vacuum to remove unreacted precursor includes:

The reaction chamber is evacuated to reduce the pressure to 10Pa or less;

Add _AlCl3 gas into the reaction chamber and maintain for 10s-20s;

Introduce purge gas into the reaction chamber, open the vacuum, and take away the unreacted _AlCl3 gas;

The pressure in the reaction chamber is reduced to 10Pa or less, and _TiF4 gas is introduced into the reaction chamber for 10s-20s;

A purge gas is introduced into the reaction chamber, and the vacuum is opened to remove the unreacted _TiF4 gas;

Repeat the above steps to obtain an aluminum fluoride protective film of a preset thickness.

The precursors of aluminum fluoride include _AlCl3 and _TiF4 . In the step of preparing the aluminum fluoride protective film, the reaction chamber is evacuated and the pressure is reduced to 10Pa or below; _AlCl3 gas is introduced into the reaction chamber and maintained for 10s-20s; purge gas is introduced into the reaction chamber, the vacuum is opened, and the unreacted _AlCl3 gas is taken away; the pressure in the reaction chamber is reduced to 10Pa or below, _TiF4 gas is introduced into the reaction chamber and maintained for 10s-20s; purge gas is introduced into the reaction chamber, the vacuum is opened, and the unreacted _TiF4 gas is taken away; the above steps are repeated to obtain an aluminum fluoride protective film of a preset thickness.

It can be understood that AlCl ₃ and TiF ₄ are solid at room temperature. In order to obtain a gaseous precursor, a temperature that can vaporize the precursor is set to vaporize the solid to obtain a gaseous precursor.

It can be understood that the step of adding AlCl ₃ gas into the reaction chamber and maintaining it for 10s-20s is to introduce a suitable amount of AlCl ₃ gas into the reaction chamber. The time for introducing the gas can be selected according to actual needs, and the present application does not specifically limit it.

Optionally, the step of introducing a lithium fluoride precursor into the reaction chamber to form a protective film on the surface of the coating and opening the vacuum to remove unreacted precursor includes:

The reaction chamber is evacuated to reduce the pressure to 10Pa or less;

Alkyl lithium vapor is introduced into the reaction chamber and maintained for 10s-20s;

Passing purge gas into the reaction chamber, opening the vacuum, and taking away unreacted alkyl lithium vapor;

The pressure in the reaction chamber is reduced to 10Pa or less, and _TiF4 vapor is introduced into the reaction chamber for 10s-20s;

A purge gas is introduced into the reaction chamber, and the vacuum is opened to remove the unreacted _TiF4 vapor;

Repeat the above steps to obtain a lithium fluoride protective film with a preset thickness.

The precursors of lithium fluoride include alkyl lithium and _TiF4 . In the step of preparing the lithium fluoride protective film, the reaction chamber is evacuated and the pressure is reduced to 10Pa or below; alkyl lithium vapor is introduced into the reaction chamber and maintained for 10s-20s; purge gas is introduced into the reaction chamber, the vacuum is opened, and the unreacted alkyl lithium vapor is taken away; the pressure in the reaction chamber is reduced to 10Pa or below, _TiF4 vapor is introduced into the reaction chamber and maintained for 10s-20s; purge gas is introduced into the reaction chamber, the vacuum is opened, and the unreacted _TiF4 vapor is taken away; the above steps are repeated to obtain a lithium fluoride protective film of a preset thickness.

Optionally, the step of preparing the positive electrode sheet includes:

Mixing the positive electrode material with the reactive substance to react, so as to form a coating layer on the surface of the positive electrode material;

The positive electrode material with the coating layer, the binder, and the conductive agent are mixed, and a solvent is added and stirred to obtain a positive electrode slurry;

Applying the positive electrode slurry to a current collector and drying it to obtain a positive electrode sheet;

Wherein, the reactive substance includes at least one of a sulfur compound and a boron compound.

Residual lithium on the surface of the positive electrode material will affect the performance of the battery. In order to remove the residual lithium, a reactive substance is used to react with the residual lithium. For example, sulfur compounds and boron compounds are mixed with the positive electrode material and reacted under certain conditions to form a coating layer on the surface of the positive electrode material; the positive electrode material with the coating layer, a binder, and a conductive agent are mixed, and a solvent is added and stirred to obtain a positive electrode slurry; the positive electrode slurry is coated on a current collector and dried to obtain a positive electrode sheet.

Optionally, the step of preparing the positive electrode sheet includes:

The positive electrode material, the binder, the conductive agent and the ammonium fluoride are mixed, and the solvent is added and stirred to obtain a positive electrode slurry;

The positive electrode slurry is coated on a current collector and dried to obtain a positive electrode sheet.

Introducing ammonium fluoride during the slurry preparation process to react with the residual lithium on the surface of the positive electrode material to form a lithium fluoride coating layer can reduce the amount of residual alkali on the surface of the positive electrode material as needed and reduce battery polarization. Compared with mixing sulfur compounds and boron compounds with positive electrode materials and reacting them under certain conditions to form a coating layer on the surface of the positive electrode material, the use of ammonium fluoride does not require additional steps. Ammonium fluoride can be added directly during the slurry preparation process, reducing process steps and improving the production efficiency of positive electrode sheets.

By converting residual lithium as a reactant into an effective lithium fluoride protective layer, the slurry gel condition is effectively improved, the residual lithium is removed, and a fast ion conductor coating is established, thereby improving the conductivity of the positive electrode sheet, reducing the polarization of the lithium-ion battery, and improving the power performance of the lithium-ion battery.

Optionally, the amount of ammonium fluoride added is in the range of 0.009% to 4.5% of the mass of the positive electrode material, preferably 0.45% to 1.1%.

In the process of removing residual lithium, the amount of ammonium fluoride to be added can be converted according to the amount of residual lithium, and the amount of ammonium fluoride added accounts for 0.009% to 4.5% of the mass of the positive electrode material, preferably 0.45% to 1.1%.

Optionally, the step of mixing the positive electrode material, the binder, the conductive agent, and ammonium fluoride, adding a solvent and stirring to obtain a positive electrode slurry includes:

The positive electrode material, binder, conductive agent and ammonium fluoride are mixed for 5-60 minutes, and a solvent is added. The mixture is stirred at a speed of 300-2000 r/min for 30-3 hours, and bubbles are removed and air is evacuated to obtain a positive electrode slurry with a solid content of 60%-85%.

In order to fully mix ammonium fluoride and positive electrode materials in the process of preparing slurry for effective reaction, during the operation, the positive electrode material, binder, conductive agent and ammonium fluoride are mixed for 5min-60min, and the solvent is added. The mixture is stirred at a speed of 300r/min to 2000r/min for 30min to 3h, and the bubbles are removed and the air is evacuated to obtain a positive electrode slurry with a solid content of 60% to 85%.

Ammonium fluoride reacts with residual lithium, and the chemical reaction equations involved are as follows: 2NH ₄ F+LiCO ₃ →2LiF↓+(NH ₄ ) ₂ CO ₃ , NH ₄ F+LiOH→LiF↓+NH ₃ ↑+H ₂ O↑.

The by-products of the reaction are all volatile or decomposed volatile substances. In order to facilitate the removal of by-products, degassing and exhaust are performed during the operation.

That is, a considerable amount of ammonium fluoride is used with residual lithium as the source, and the ammonium fluoride and the positive electrode material are fully contacted, mixed and reacted under the slurry stirring conditions. After the stirring is completed, part of the gas product is removed by exhausting the gas in the defoaming stage.

Optionally, the step of applying the positive electrode slurry to a current collector and drying to obtain a positive electrode sheet includes:

The positive electrode slurry is coated on a current collector and dried at a temperature of 100° C. to 170° C. to obtain a positive electrode sheet.

In order to effectively ensure the decomposition and removal of the reaction by-product (NH ₄ ) ₂ CO ₃ , the ammonium carbonate is decomposed and removed by adjusting the drying temperature during the drying process. The drying temperature is 100°C-170°C. Under this drying condition, the product (NH ₄ ) ₂ CO ₃ is decomposed and discharged through the airway, which is conducive to the rapid decomposition and removal of (NH ₄ ) ₂ CO ₃ and improves production efficiency.

Optionally, the mass of residual lithium in the positive electrode material accounts for a proportion of the mass of the positive electrode material that satisfies Li ₂ CO ₃ ≥ 0.02%, and LiOH ≥ 0.2%.

In order to prepare a coating layer with suitable coating quality so that the beneficial effect of the coating layer is obvious, the mass of residual lithium in the positive electrode material accounts for the mass of the positive electrode material and satisfies Li ₂ CO ₃ ≥ 0.02% and LiOH ≥ 0.2%.

The present application also provides an electrode assembly, which includes the positive electrode plate as described, or includes the positive electrode plate prepared by the preparation method of the positive electrode plate as described.

The present application also provides a battery cell, which includes the electrode assembly as described above.

The present application also provides a battery, which includes the battery cell as described above.

The present application also provides an electrical device, which includes the battery cell or the battery as described above.

The positive electrode sheet of the present application includes a current collector and a coating disposed on at least one side of the current collector, and a protective film is disposed on the surface of the coating, and the material of the protective film includes fluoride. Considering that the positive electrode material in the coating will lead to performance degradation when it contacts the air, and that the positive electrode material will have an interface side reaction when it contacts the electrolyte, in order to improve the performance of the positive electrode material, a protective film is disposed on the surface of the coating to reduce the chance of the positive electrode material contacting the air, and reduce the probability of the positive electrode material and the electrolyte having an interface reaction, thereby improving the stability of the positive electrode material and improving the performance of the battery.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

FIG1 is a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application;

FIG2 is a schematic diagram of the structure of a positive electrode sheet according to an embodiment of the present application;

FIG3 is a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application;

FIG4 is a schematic diagram of a process for preparing a positive electrode sheet according to an embodiment of the present application;

FIG5 is a schematic diagram of a secondary battery according to an embodiment of the present application;

FIG6 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG5 ;

FIG7 is a schematic diagram of a battery module according to an embodiment of the present application;

FIG8 is a schematic diagram of a battery pack according to an embodiment of the present application;

FIG9 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG8 ;

FIG. 10 is a schematic diagram of an electric device using a secondary battery according to an embodiment of the present application as a power source.

Description of Figure Numbers:

Label name Label name 100 Positive electrode 2 Upper box 10 Current Collector 3 Lower box 20 Active layer 4 Battery Module 30 Protective film 5 Secondary battery 30a Lithium fluoride protective film 51 case 30b Aluminum fluoride protective film 52 Electrode assembly 1 Battery Pack 53 Top cover assembly

The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings.

DETAILED DESCRIPTION

The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

Hereinafter, the cathode electrode sheet, electrode assembly, battery cell, battery cell, battery and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

"Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "a-b" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

The presence of impurities on the surface of the positive electrode material may reduce the performance of the positive electrode material.

For example, when preparing high-nickel ternary materials, there are structural stability problems during the synthesis process. Therefore, in order to synthesize in a stable oxide form, an excess of Li/Me (alloy element) conditions are usually designed to synthesize a positive electrode active material with a stable structure. That is, in the process of preparing high-nickel ternary materials, the lithium salt is excessive in the mixed ternary precursor and lithium salt. The excess of lithium salt makes the excess part of the lithium salt not participate in the reaction, so that this part of the lithium salt will react with moisture and _CO2 in the air to generate residual lithium (LiOH and _Li2CO3 ). When manufacturing battery cells, the presence of residual _lithium will cause many problems. For example, the residual lithium has poor ion conductivity. It is formed on the surface of the ternary material, which will hinder the transmission of lithium ions in the ternary material. In addition, _Li2CO3 will react with the _electrolyte to generate gas and heat, affecting the safety of the battery.

Applying positive electrode materials with residual lithium to the coating will reduce the performance of the battery. For example, considering the performance degradation caused by the positive electrode material in the coating contacting with air and the interfacial side reactions caused by the positive electrode material contacting with the electrolyte.

In order to solve the above problems, the present application provides a positive electrode plate, which includes a current collector and a coating provided on at least one side of the current collector, a surface of the coating is provided with a protective film, and the material of the protective film includes fluoride.

The current collector refers to the structure or part that collects current. In lithium-ion batteries, it mainly refers to metal foil, such as copper foil and aluminum foil. The current collector is used as a substrate to attach the positive or negative active material, and plays the role of collecting the current generated by the active material and outputting a large current to the outside. Generally, aluminum foil is used as the positive current collector, and copper foil is used as the negative current collector.

The coating layer includes a positive electrode material, a binder, and a conductive agent. In the process of preparing the coating layer, the positive electrode material, the binder, the conductive agent and a solvent are mixed to prepare a slurry, and the prepared slurry is coated on the current collector to obtain the coating layer.

The positive electrode material can provide a lithium source and is used in batteries. During charging, lithium ions are released from the lattice of the positive electrode active material and inserted into the lattice of the negative electrode material after passing through the electrolyte; during discharging, lithium ions are released from the lattice of the negative electrode material and inserted into the lattice of the positive electrode material after passing through the electrolyte.

Binder refers to a material with adhesive properties that is used to bond different substances together.

Conductive agent is used to ensure that the electrode has good charge and discharge performance. A certain amount of conductive material is usually added during the production of the electrode. It collects microcurrents between active materials and between active materials and current collectors to reduce the contact resistance of the electrode and accelerate the movement rate of electrons. It can also effectively increase the migration rate of lithium ions in the electrode material, thereby improving the charge and discharge efficiency of the electrode.

The protective film is a film structure arranged on the surface of the coating. As shown in FIG1 , the positive electrode sheet 100 includes a current collector 10, a coating 20 arranged on the current collector 10, and a protective film 30 arranged on the surface of the coating 20. It can be understood that the surface of the coating 20 refers to the surface of the coating exposed to the outside, for example, it can be the surface of the coating 20 away from the current collector, or it can be the surface located on the side of the coating 20. The protective film 30 can be arranged on any surface of the coating 20, and it is specifically arranged according to the needs. For example, in one case, the protective film 30 is arranged on each surface of the coating exposed to the outside to reduce the contact between the coating and the electrolyte.

Fluoride refers to a compound containing negatively charged fluorine.

Fluoride can effectively reduce the oxidation activity of the positive electrode material surface, inhibit the oxidative decomposition of the electrolyte at the positive electrode, and promote the lithium ion transport in the solid phase. For example, the fluoride can be lithium fluoride or aluminum fluoride, among which lithium fluoride is more beneficial for improving its air stability.

That is, in order to improve the performance of the coating, a protective film is set on the surface of the coating. The material of the protective film includes fluoride, which reduces the chance of contact between the positive electrode material in the coating and the air, and reduces the probability of interfacial reaction between the positive electrode material and the electrolyte, thereby improving the stability of the positive electrode material and thus improving the performance of the battery.

Moreover, lithium fluoride or aluminum fluoride is an ion conductor, which will not block the transmission of lithium ions or affect the wetting.

In one embodiment, the thickness of the protection film ranges from 1 nm to 50 nm, preferably from 5 nm to 20 nm.

In order to make the protective film effectively reduce the chance of contact between the electrolyte and the coating and ensure that the lithium ions have a good migration rate, the thickness of the protective film ranges from 1 nm to 50 nm, preferably from 5 nm to 20 nm.

In the above-mentioned 1nm to 50nm, the values include the minimum and maximum values of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values in the embodiments and 1nm, 3nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, etc.

In the above 5nm to 20nm, the values include the minimum and maximum values of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values in the embodiments and 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, etc.

In one embodiment, the fluoride includes at least one of lithium fluoride and aluminum fluoride.

The fluoride includes at least one of lithium fluoride and aluminum fluoride. That is, the protective film may include lithium fluoride and aluminum fluoride at the same time, or may be independently composed of lithium fluoride or aluminum fluoride. Of course, in some cases, other types of materials may be added to the protective film as needed, which is not limited in this application and can be designed according to usage requirements.

Lithium fluoride, an inorganic substance with the chemical formula LiF, is an alkali metal halide. It is a white crystal at room temperature and is insoluble in water.

Aluminum fluoride, an inorganic substance, has the chemical formula AlF ₃ , is insoluble in water, acid and alkali, and is very stable.

Lithium fluoride and aluminum fluoride are ion-conducting substances, which are conducive to the transmission of lithium ions. For example, lithium fluoride is an electronic insulator, and its ion conductivity is about 10 ^-13 Scm ^-1 -10 ^-14 Scm ^-1 .

The specific type of fluoride in the present application is not limited, as long as it can be set on the surface of the coating, reduce the chance of contact between the positive electrode material and the air in the coating, and reduce the probability of interfacial reaction between the positive electrode material and the electrolyte.

In one embodiment, the protective film includes a lithium fluoride protective film and an aluminum fluoride protective film, and the lithium fluoride protective film and the aluminum fluoride protective film are stacked on the surface of the coating; and/or, the protective film includes a lithium fluoride protective film and an aluminum fluoride protective film, at least a portion of the surface of the coating is provided with the lithium fluoride protective film, and at least another portion of the surface of the coating is provided with the aluminum fluoride protective film.

The lithium fluoride protective film and the aluminum fluoride protective film are stacked on the surface of the coating. As shown in Figure 3, the lithium fluoride protective film 30a and the aluminum fluoride protective film 30b are alternately arranged on the surface of the coating 20. For example, the lithium fluoride protective film 30a is arranged on the surface of the coating 20, and the aluminum fluoride protective film 30b is arranged on the side of the lithium fluoride protective film 30a away from the coating 20. Of course, the aluminum fluoride protective film 30b can also be arranged on the surface of the coating 20, and the lithium fluoride protective film 30a is arranged on the side of the aluminum fluoride protective film 30b away from the coating 20. The number of layers of the lithium fluoride protective film 30a and the aluminum fluoride protective film 30b is not specifically limited. For example, the lithium fluoride protective film 30a has two layers, and the aluminum fluoride protective film 30b has one layer. The aluminum fluoride protective film 30b is arranged between the two layers of the lithium fluoride protective film 30a, which can be arranged according to needs.

At least a portion of the surface of the coating is provided with a lithium fluoride protective film, and at least another portion of the surface of the coating is provided with an aluminum fluoride protective film. As shown in FIG2 , at least a portion of the surface of the coating 20 is provided with a lithium fluoride protective film 30a, and at least another portion of the surface of the coating 20 is provided with an aluminum fluoride protective film 30b. It can be understood that the lithium fluoride protective film 30a and the aluminum fluoride protective film 30b can be arranged side by side on one surface of the coating 20 without any specific limitation, and can be considered as needed.

The protective film includes a lithium fluoride protective film and an aluminum fluoride protective film, that is, the protective film includes both lithium fluoride and aluminum fluoride protective films. The thickness ratio of the lithium fluoride and aluminum fluoride protective films is not limited and can be set according to needs. For example, the film thickness of lithium fluoride and aluminum fluoride can be 1:1. Both lithium fluoride and aluminum fluoride can effectively reduce the oxidation activity on the surface of the positive electrode material, inhibit the oxidative decomposition of the electrolyte at the positive electrode, and promote the lithium ion transport in the solid phase. Among them, lithium fluoride is more beneficial for improving its air stability. When the coating is sensitive to air, the thickness of lithium fluoride can be increased.

In one embodiment, the coating layer includes a positive electrode material, a coating layer is formed on the surface of the positive electrode material, and the coating layer includes at least one of a sulfur-containing compound, a boron-containing compound, and a fluoride.

The sulfur-containing compound can react with the residual lithium, for example, it can be K ₂ S ₂ O ₃ or Na ₂ S ₂ O ₃ .

The boron-containing compound can react with the residual lithium, for example, it can be B ₂ O ₃ .

Positive electrode materials, for example, ternary positive electrode materials, especially the higher the nickel content, the higher the residual lithium compounds on the surface during the synthesis process. Such surface residual lithium can easily absorb carbon dioxide and water in the air, forming _Li2CO3 and LiOH _layers on the particle surface, which will have the following effects: it consumes the Li in the material and has no electrochemical activity, thus causing capacity decay; LiOH will react with polyvinylidene fluoride PVDF to cause gelation of the slurry, and the LiOH remaining on the electrode may also react with the electrolyte _LiPF6 to consume the Li ions in the electrolyte and produce HF, which will further corrode the positive electrode material and alienate its surface; the dense _Li2CO3 layer on the surface of the positive electrode particles will also hinder the diffusion of Li in the _future , affecting the battery's electrical performance.

In order to solve the above problems, the residual lithium compounds are reduced or eliminated through chemical reactions, and an ion-conductive coating layer is formed on the surface of the positive electrode material to reduce battery polarization. The coating layer includes at least one of sulfur-containing compounds, boron-containing compounds, and fluorides.

It can be understood that the residual lithium compound in the positive electrode material can be reacted with the sulfur-containing compound, the boron-containing compound, the ammonium fluoride and the like. For example, the sulfur-containing compound is used to react with the residual _lithium ( _LiOH and _{Li2CO3 )} to reduce the content of _{residual lithium} and _increase the ion-conducting substance _. The sulfur compound includes _K2SxOy or _Na2SxOy (x= _1-8 , _y =1-8). For example, _{it can} be _K2S2O3 or _Na2S2O3 . _The reaction formula is nLiOH+ _nK2SxOy- > _nLi2S + _nLi2SOx + _nH2O ( _{n =} integer) _{; nLi2CO3} + _{nK2SxOy- >} nK2CO3+nLi2SxOy ( _n = _integer ) _{; nLiOH} + _{nNa2SxOy- > nLi2S + nLi2SOx} + _{nH2O .} O (n=integer); nLi ₂ CO ₃ +nNa ₂ S _x O _y ->nNa ₂ CO ₃ +nLi ₂ S _x O _y (n=integer).

Boron compounds are used to react with residual lithium (LiOH and _Li2CO3 ) to reduce the content of residual _lithium and increase ion-conducting substances. Boron compounds _{include H3BO3} or _{B2O3 .} The reaction _formula is nLiOH+ _nB2O3- > _nLi3BO3 + _nH2O ( _n = _integer ); _{nLi2CO3 + nB2O3-} > _nLi3BO3 + _{nCO2 (} n=integer).

Ammonium fluoride is used to react with residual lithium (LiOH and Li ₂ CO ₃ ) to reduce or eliminate residual lithium and increase ion-conducting substances, 2NH ₄ F+Li ₂ CO ₃ ->2LiF↓+(NH ₄ ) ₂ CO ₃ , NH ₄ F+LiOH->LiF↓+NH ₃ ↑+H ₂ O↑.

Considering that although the ternary material is modified and coated during the material production process, the basic residual lithium characterization at the material level shows that there is still a certain amount of residual lithium present, and these residual lithium will still be exposed to the air during the subsequent preparation of the battery, such reactions will continue to exist and the impact on performance will continue to exist, this application introduces two protection steps in the preparation process of the positive electrode plate to achieve the ultimate all-round protection of the positive electrode plate.

The first step is to form a coating layer on the surface of the positive electrode material, and the second step is to use the atomic layer deposition process to build a protective film on the surface of the positive electrode.

It is understandable that the coating layer depends on the distribution of residual lithium on the surface of the original ternary material. If there is no residual lithium in this area, the protective film cannot be formed through chemical reaction. Therefore, a double protection process is adopted. The second protective film can effectively protect the positive electrode material that is not coated with the coating layer, and effectively inhibit the performance degradation caused by the contact of the positive electrode surface with the air in the subsequent process. It can also reduce the probability of interfacial side reactions between the positive electrode and the electrolyte. The composite protective layer constructed by the two processes can further protect the structural stability of the positive electrode material during deep lithium deintercalation.

It can be understood that the second step is to use the atomic layer deposition process to construct a nano-scale protective film on the surface of the positive electrode, which can achieve a dense and uniform film layer without affecting the energy density due to the thickness like traditional gravure coating.

In one embodiment, the coating layer is lithium fluoride.

The coating layer is lithium fluoride obtained by reacting ammonium fluoride. The residual lithium can be completely removed by controlling the amount of ammonium fluoride added to the reaction. And controlling the operation steps can effectively remove the reaction by-products, thus avoiding the introduction of new impurities.

Furthermore, the step of adding ammonium fluoride can be performed during the process of preparing the coating slurry without adding additional steps, thereby improving the preparation efficiency of the positive electrode sheet.

In one embodiment, the mass percentage of lithium fluoride to the total mass of the positive electrode material is 0.01% to 5%, preferably 0.5% to 1.2%.

The total mass of the positive electrode material is the sum of the mass of the positive electrode material and the mass of lithium fluoride. For example, the mass of lithium fluoride is m1, and the mass of the positive electrode material is m2. The mass percentage of lithium fluoride in the total mass of the positive electrode material is calculated as m1/(m1+m2)×100%.

In the process of obtaining a lithium fluoride coating layer by reacting residual lithium with ammonium fluoride, the amount of ammonium fluoride to be added can be converted according to the amount of residual lithium in the positive electrode material to completely react the residual lithium. In the obtained positive electrode material, the mass percentage of lithium fluoride to the total mass of the positive electrode material is 0.01% to 5%, preferably 0.5% to 1.2%.

In the above-mentioned 0.01% to 5%, the values include the minimum and maximum values of the range, and every value between such minimum and maximum values. Specific examples include but are not limited to the point values in the embodiments and 0.01%, 0.05%, 0.1%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc.

In the above 0.5% to 1.2%, the values include the minimum and maximum values of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values in the embodiments and 0.5%, 0.7%, 0.9%, 1%, 1.2%, etc.

In one embodiment, the general formula of the positive electrode material in the coating is Li _x Ni _y M _1-y O ₂ , 0.9≤x≤1.15, 0.6≤y≤1, and M is selected from one or more of Co, Mn, and Al; and/or, the general formula of the positive electrode material in the coating is xLi ₂ MnO ₃ .(1-x)LiMO ₂ , 0.1≤x≤0.9, and M is selected from one or more of Co, Mn, and Al.

The positive electrode material in the coating includes Li _x Ni _y M _1-y O ₂ with a layered structure, 0.9≤x≤1.15, 0.6≤y≤1, M is selected from one or more of Co, Mn, and Al, and/or includes lithium-rich manganese-based positive electrode material xLi ₂ MnO ₃ .(1-x)LiMO ₂ , 0.1≤x≤0.9, M is selected from one or more of Co, Mn, and Al.

In one embodiment, the present application also provides a method for preparing a positive electrode plate, comprising: preparing a positive electrode plate; preparing a fluoride precursor; and forming a protective film on the coating surface of the positive electrode plate by thin film deposition technology.

Thin film deposition technology, including chemical vapor deposition and physical vapor deposition.

Chemical vapor deposition is a chemical technology that mainly uses one or more gas phase compounds or single substances containing thin film elements to form thin films through chemical reactions on the substrate surface. For example, it includes atomic layer deposition process.

Physical vapor deposition, physical vapor deposition technology refers to the technology of using physical methods under vacuum conditions to vaporize the surface of the material source (solid or liquid) into gaseous atoms or molecules, or partially ionize into ions, and deposit a thin film with some special functions on the surface of the substrate through a low-pressure gas (or plasma) process. Examples include vacuum evaporation, sputtering, arc plasma coating, ion plating and molecular beam epitaxy.

In order to form a protective film on the coating surface of the positive electrode plate, the steps include preparing the positive electrode plate, preparing a fluoride precursor, and forming a protective film on the coating surface of the positive electrode plate by thin film deposition technology.

In one embodiment, the thin film deposition technique includes an atomic layer deposition process.

Atomic layer deposition, atomic layer deposition is a method (technology) of forming a deposited film by alternately passing gaseous precursor pulses into the reactor and chemically adsorbing and reacting on the deposition substrate. When the precursors reach the surface of the deposition substrate, they will chemically adsorb on its surface and react on the surface. The atomic layer deposition reactor needs to be cleaned with an inert gas between the precursor pulses.

In order to make the prepared protective film better, the atomic layer deposition process is preferably selected. The atomic layer deposition process has better chemical ratio, strong stress control ability, smooth film surface, wide process window range, and wider range of precursor selection.

For example, in one embodiment, in order to form a protective film on the positive electrode plate, the positive electrode plate is prepared, and the protective film is formed on the surface of the coating using an atomic layer deposition process. A nanoscale protective film is constructed on the surface of the coating using an atomic layer deposition process, which can achieve a dense and uniform film layer without affecting the energy density due to the thickness as in traditional gravure coating.

In one embodiment, the fluoride includes lithium fluoride and/or aluminum fluoride.

Fluoride can effectively reduce the oxidation activity of the positive electrode material surface, inhibit the oxidative decomposition of the electrolyte at the positive electrode, and promote the lithium ion transport in the solid phase. A fluoride protective film is formed on the coating surface of the positive electrode sheet by preparing a fluoride precursor and using thin film deposition technology. The fluoride precursor includes a lithium fluoride precursor and/or an aluminum fluoride precursor.

In one embodiment, the step of forming a coating layer on the coating surface of the positive electrode plate by an atomic layer deposition process includes: placing the positive electrode plate into an atomic layer deposition reaction chamber, evacuating the chamber, and setting the deposition temperature to 200°C-250°C; introducing a suitable fluoride precursor into the reaction chamber to form a protective film on the surface of the coating, opening the vacuum to remove unreacted precursors, and repeating the above steps to obtain a protective film of a preset thickness.

The material of the protective film includes fluoride, and the type of fluoride is not specifically limited. The precursor can be selected according to the selected fluoride type. The step of forming a coating layer on the coating surface of the positive electrode plate by atomic layer deposition process includes: placing the positive electrode plate into the atomic layer deposition reaction chamber, evacuating the chamber, and setting the deposition temperature to 200℃-250℃; introducing a suitable fluoride precursor into the reaction chamber to form a protective film on the surface of the coating, opening the vacuum to remove unreacted precursor, and repeating the above steps to obtain a protective film of preset thickness.

During the preparation of the protective film, it is necessary to maintain a vacuum environment to prevent active substances in the air from participating in the reaction during the film formation process and affecting the quality of the film layer. Therefore, the positive electrode plate needs to be placed in the reaction chamber and evacuated so that the protective film can be prepared in a vacuum environment.

In the above 200℃-250℃, the values include the minimum and maximum values of the range, and every value between the minimum and maximum values. Specific examples include but are not limited to the point values in the embodiments and 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, etc.

In one embodiment, the steps of introducing a suitable fluoride precursor into a reaction chamber to form a protective film on the surface of the coating, opening the vacuum to remove unreacted precursor, and repeating the above steps to obtain a protective film of a preset thickness include: introducing an aluminum fluoride precursor into the reaction chamber to form a protective film on the surface of the coating, opening the vacuum to remove unreacted precursor; introducing a lithium fluoride precursor into the reaction chamber to form a protective film on the surface of the coating, opening the vacuum to remove unreacted precursor; and repeating the above steps to obtain a protective film of a preset thickness.

The fluoride includes at least one of lithium fluoride and aluminum fluoride. In order to obtain a protective film of lithium fluoride and aluminum fluoride, a suitable fluoride precursor is introduced into a reaction chamber to form a protective film on the surface of the coating, the vacuum is opened to remove the unreacted precursor, and the above steps are repeated to obtain a protective film of a preset thickness, which includes: introducing an aluminum fluoride precursor into the reaction chamber to form a protective film on the surface of the coating, and the vacuum is opened to remove the unreacted precursor; introducing a lithium fluoride precursor into the reaction chamber to form a protective film on the surface of the coating, and the vacuum is opened to remove the unreacted precursor; and repeating the above steps to obtain a protective film of a preset thickness.

In one embodiment, the steps of introducing an aluminum fluoride precursor into a reaction chamber, forming a protective film on the surface of the coating, and opening the vacuum to remove unreacted precursor include: evacuating the reaction chamber to reduce the pressure to 10Pa or less; introducing _AlCl3 gas into the reaction chamber and maintaining it for 10s-20s; introducing purge gas into the reaction chamber, opening the vacuum, and taking away unreacted _AlCl3 gas; reducing the pressure in the reaction chamber to 10Pa or less, introducing _TiF4 gas into the reaction chamber and maintaining it for 10s-20s; introducing purge gas into the reaction chamber, opening the vacuum, and taking away unreacted _TiF4 gas; repeating the above steps to obtain an aluminum fluoride protective film of a preset thickness.

The precursors of aluminum fluoride include _AlCl3 and _TiF4 . In the step of preparing the aluminum fluoride protective film, the reaction chamber is evacuated and the pressure is reduced to 10Pa or below; _AlCl3 gas is introduced into the reaction chamber and maintained for 10s-20s; purge gas is introduced into the reaction chamber, the vacuum is opened, and the unreacted _AlCl3 gas is taken away; the pressure in the reaction chamber is reduced to 10Pa or below, _TiF4 gas is introduced into the reaction chamber and maintained for 10s-20s; purge gas is introduced into the reaction chamber, the vacuum is opened, and the unreacted _TiF4 gas is taken away; the above steps are repeated to obtain an aluminum fluoride protective film of a preset thickness.

It can be understood that AlCl ₃ and TiF ₄ are solid at room temperature. In order to obtain a gaseous precursor, a temperature that can vaporize the precursor is set to vaporize the solid to obtain a gaseous precursor.

It can be understood that the step of adding AlCl ₃ gas into the reaction chamber and maintaining it for 10s-20s is to introduce a suitable amount of AlCl ₃ gas into the reaction chamber. The time for introducing the gas can be selected according to actual needs, and the present application does not specifically limit it.

The purpose of introducing a purge gas into the reaction chamber is to remove other unreacted gases or impurities. The purge gas is an inert gas, such as argon.

In one embodiment, the steps of introducing a lithium fluoride precursor into a reaction chamber, forming a protective film on the surface of the coating, and opening the vacuum to remove unreacted precursor include: evacuating the reaction chamber to reduce the pressure to 10Pa or less; introducing alkyl lithium vapor into the reaction chamber and maintaining it for 10s-20s; introducing purge gas into the reaction chamber, opening the vacuum, and taking away unreacted alkyl lithium vapor; reducing the pressure in the reaction chamber to 10Pa or less, introducing _TiF4 vapor into the reaction chamber and maintaining it for 10s-20s; introducing purge gas into the reaction chamber, opening the vacuum, and taking away unreacted _TiF4 vapor; repeating the above steps to obtain a lithium fluoride protective film of a preset thickness.

The precursors of lithium fluoride include alkyl lithium and _TiF4 . In the step of preparing the lithium fluoride protective film, the reaction chamber is evacuated and the pressure is reduced to 10Pa or below; alkyl lithium vapor is introduced into the reaction chamber and maintained for 10s-20s; purge gas is introduced into the reaction chamber, the vacuum is opened, and the unreacted alkyl lithium vapor is taken away; the pressure in the reaction chamber is reduced to 10Pa or below, _TiF4 vapor is introduced into the reaction chamber and maintained for 10s-20s; purge gas is introduced into the reaction chamber, the vacuum is opened, and the unreacted _TiF4 vapor is taken away; the above steps are repeated to obtain a lithium fluoride protective film of a preset thickness.

The alkyl lithium can be lithium tert-butoxide, butyl lithium, phenyl lithium, etc. For example, lithium tert-butoxide and TiF4 are solid at _room temperature. In order to obtain a gaseous precursor, a temperature that can vaporize the precursor is set to vaporize the solid to obtain a gaseous precursor.

In one embodiment, the steps of preparing a positive electrode plate include: mixing a positive electrode material with a reactive substance to react, so as to form a coating layer on the surface of the positive electrode material; mixing the positive electrode material with the coating layer, a binder, and a conductive agent, adding a solvent for stirring, and obtaining a positive electrode slurry; coating the positive electrode slurry on a current collector, and drying to obtain a positive electrode plate; wherein the reactive substance includes at least one of a sulfur compound and a boron compound.

For example, sulfur compounds and boron compounds are mixed with positive electrode materials and reacted under certain conditions to form a coating layer on the surface of the positive electrode material; the positive electrode material with the coating layer, a binder, and a conductive agent are mixed, and a solvent is added for stirring to obtain a positive electrode slurry; the positive electrode slurry is coated on a current collector and dried to obtain a positive electrode sheet.

In one embodiment, the step of preparing the positive electrode sheet includes: mixing the positive electrode material, the binder, the conductive agent, and ammonium fluoride, adding a solvent and stirring to obtain a positive electrode slurry; coating the positive electrode slurry on a current collector, and drying to obtain a positive electrode sheet.

Introducing ammonium fluoride during the slurry preparation process to react with the residual lithium on the surface of the positive electrode material to form a lithium fluoride coating layer can reduce the amount of residual alkali on the surface of the positive electrode material as needed and reduce battery polarization. Compared with mixing sulfur compounds and boron compounds with positive electrode materials and reacting them under certain conditions to form a coating layer on the surface of the positive electrode material, the use of ammonium fluoride does not require additional steps. Ammonium fluoride can be added directly during the slurry preparation process, reducing process steps and improving the production efficiency of positive electrode sheets.

By converting residual lithium as a reactant into an effective lithium fluoride protective layer, the slurry gel condition is effectively improved, the residual lithium is removed, and a fast ion conductor coating is established, thereby improving the conductivity of the positive electrode sheet, reducing the polarization of the lithium-ion battery, and improving the power performance of the lithium-ion battery.

In one embodiment, the amount of ammonium fluoride added is in the range of 0.009% to 4.5% by mass of the positive electrode material, preferably 0.45% to 1.1%.

For example, the added mass of ammonium fluoride is M1, and the mass of the positive electrode material is M2. Then the calculation formula for the added amount of ammonium fluoride to the mass of the positive electrode material is M1/M2×100%.

The residual lithium content in the positive electrode material can be measured by hydrochloric acid titration, and the mass of ammonium fluoride to be added can be calculated by the measured residual lithium content. The amount of ammonium fluoride added accounts for 0.009% to 4.5% of the mass of the positive electrode material, preferably 0.45% to 1.1%.

In the above-mentioned 0.009% to 4.5%, the values include the minimum and maximum values of the range, and every value between such minimum and maximum values. Specific examples include but are not limited to the point values in the embodiments and 0.009%, 0.01%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4.5%, etc.

In the above-mentioned 0.45% to 1.1%, the values include the minimum and maximum values of the range, and every value between such minimum and maximum values. Specific examples include but are not limited to the point values in the embodiments and 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1.0%, 1.1%, etc.

In one embodiment, the step of mixing the positive electrode material, the binder, the conductive agent, and ammonium fluoride, adding the solvent for stirring, and obtaining the positive electrode slurry includes: mixing the positive electrode material, the binder, the conductive agent, and the ammonium fluoride for 5 min-60 min, adding the solvent, stirring at a speed of 300 r/min to 2000 r/min for 30 min to 3 h, removing bubbles and exhausting air to obtain a positive electrode slurry with a solid content of 60%-85%.

In order to fully mix ammonium fluoride and positive electrode materials in the process of preparing slurry for effective reaction, during the operation, the positive electrode material, binder, conductive agent and ammonium fluoride are mixed for 5min-60min, and the solvent is added. The mixture is stirred at a speed of 300r/min to 2000r/min for 30min to 3h, and the bubbles are removed and the air is evacuated to obtain a positive electrode slurry with a solid content of 60% to 85%.

Ammonium fluoride reacts with residual lithium, and the chemical reaction equations involved are as follows: 2NH ₄ F+LiCO ₃ →2LiF↓+(NH ₄ ) ₂ CO ₃ , NH ₄ F+LiOH→LiF↓+NH ₃ ↑+H ₂ O↑.

The by-products of the reaction are all volatile or decomposed volatile substances. In order to facilitate the removal of by-products, degassing and exhaust are performed during the operation.

That is, a considerable amount of ammonium fluoride is used with residual lithium as the source, and the ammonium fluoride and the positive electrode material are fully contacted, mixed and reacted under the slurry stirring conditions. After the stirring is completed, part of the gas product is removed by exhausting the gas in the defoaming stage.

In one embodiment, the step of applying the positive electrode slurry to the current collector and drying to obtain the positive electrode sheet includes: applying the positive electrode slurry to the current collector and drying at a temperature of 100° C.-170° C. to obtain the positive electrode sheet.

In order to effectively ensure the decomposition and removal of the reaction by-product (NH ₄ ) ₂ CO ₃ , the ammonium carbonate is decomposed and removed by adjusting the drying temperature during the drying process. The drying temperature is 100°C-170°C. Under this drying condition, the product (NH ₄ ) ₂ CO ₃ is decomposed and discharged through the airway, which is conducive to the rapid decomposition and removal of (NH ₄ ) ₂ CO ₃ and improves production efficiency.

In one embodiment, the mass of residual lithium in the positive electrode material accounts for the mass of the positive electrode material and satisfies Li ₂ CO ₃ ≥ 0.02%, LiOH ≥ 0.2%.

In order to prepare a coating layer with suitable coating quality so that the beneficial effect of the coating layer is obvious, the mass of residual lithium in the positive electrode material accounts for the mass of the positive electrode material and satisfies Li ₂ CO ₃ ≥ 0.02% and LiOH ≥ 0.2%.

A full range of protective films are formed on the surface of the positive electrode material and the surface and depth of the positive electrode sheet. The technical effects of the protective film are as follows:

The present application converts residual lithium as a reactant into an effective coating layer, effectively improves the gelation of the slurry, removes residual lithium, establishes a fast ion conductor coating layer, improves the conductivity of the positive electrode plate, reduces the polarization of the lithium-ion battery, and improves the power performance of the lithium-ion battery; and on the basis of the coating layer, adds a protective film of lithium fluoride and/or aluminum to protect the positive electrode from interfacial side reactions with the electrolyte. The composite protective layer constructed by the two processes can further protect the structural stability and surface stability of the positive electrode material during deep lithium deintercalation, which is beneficial to improving the life of the battery.

In one embodiment, the present application further provides an electrode assembly, which includes the positive electrode plate as described above, or includes a positive electrode plate made by the method for making the positive electrode plate as described above.

Since the positive electrode plate adopts all the technical solutions of all the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

In one embodiment, the present application further provides a battery cell, which includes the electrode assembly as described above.

Since the electrode assembly adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

In one embodiment, the present application further provides a battery, which includes the battery cell as described above.

Since the battery cell adopts all the technical solutions of all the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

In one embodiment, the present application further provides an electrical device, which includes the battery cell or battery described above.

Since the battery cell or battery adopts all the technical solutions of all the above embodiments, it at least has all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

In addition, the battery (secondary battery, battery module, battery pack) and the electric device of the present application will be described below with reference to the drawings as appropriate.

In one embodiment of the present application, a secondary battery is provided.

Typically, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through. The separator is the separator improved above in this application.

The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector.

As an example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, when the secondary battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material for lithium-ion batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: an olivine-structured lithium-containing phosphate, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO ₂ ), lithium nickel oxide (such as LiNiO ₂ ), lithium manganese oxide (such as LiMnO ₂ , LiMn ₂ O ₄ ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi _1/3 Co _{1/ 3} Mn _1/3 O ₂ (also referred to as NCM ₃₃₃ ), LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also referred to as NCM ₅₂₃ ), LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also referred to as NCM ₂₁₁ ), LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (also referred to as NCM ₆₂₂ ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), and LiNi _0.8 Co _0.2 Mn _0.2 O ₂ (also referred to as NCM ₈₁₁ ), lithium nickel cobalt aluminum oxide (such as LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) and modified compounds thereof. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO ₄ (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO ₄ ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

In some embodiments, the positive electrode film layer may further include a conductive agent, for example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the negative electrode active material may adopt the negative electrode active material for the battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs.

In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

In some embodiments, the material of the diaphragm can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular limitation. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly by a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. For example, FIG5 is a secondary battery 5 of a square structure as an example.

In some embodiments, referring to FIG. 6 , the outer package may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the diaphragm can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

FIG7 is a battery module 4 as an example. Referring to FIG7 , in the battery module 4, a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

FIG8 and FIG9 are battery packs 1 as an example. Referring to FIG8 and FIG9 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

In addition, the present application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

As an electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

Fig. 10 is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery may be used as a power source.

Example

Example 1

Cathode slurry preparation:

The positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , the binder PVDF, and the conductive agent carbon black are mixed in a ratio of 90:5:5, and the corresponding ammonium fluoride is added according to the residual lithium content (the percentage of residual alkali in the positive electrode material is 0.2%, and the mass of the added ammonium fluoride accounts for 0.18% of the mass of the positive electrode material). After dry mixing for 15 minutes, NMP is added and stirred at a high speed of 1000 rpm for 120 minutes, and then defoamed and exhausted to finally obtain a uniform positive electrode slurry with a solid content of 70%.

Positive electrode preparation

The positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil, and the oven temperature was set to 130°C to dry the electrode piece; then an aluminum fluoride film layer was deposited on the positive electrode piece using an atomic layer deposition device, the precursor A was ground TiF ₄ , the precursor B was AlCl ₃ , and the deposition temperature was 250°C. The positive electrode piece is placed in the atomic layer deposition ALD reaction chamber, and the deposition parameters and deposition process are as follows: 1) evacuate the reaction chamber until the pressure drops below 10Pa; 2) open the valve of precursor A, put _AlCl3 vapor into the reaction chamber, and maintain it for 15 seconds, and the temperature of the generated vapor is 120°C; 3) introduce argon gas into the reaction chamber for 120 seconds, then open the vacuum and take away the unreacted precursor A; 4) wait for the pressure in the reaction chamber to drop to 10Pa, open the valve of precursor B, introduce _TiF4 vapor into the reaction chamber, and maintain it for 15 seconds, and the temperature of the generated vapor is 120°C; 5) introduce argon gas into the reaction chamber for 100 seconds, then open the vacuum and take away the unreacted precursor B; from 1) to 5) is a complete cycle process, and the above cycle is repeated to obtain a protective film with a thickness of about 10nm; the electrode piece treated with the protective film is subjected to cold pressing, slitting and other processes to obtain an assembleable positive electrode piece.

Battery components and finished product preparation

The negative electrode material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are fully stirred and mixed in a deionized water solvent system in a mass ratio of 90:5:2:2:1, and then coated on the negative electrode collector copper foil, and after drying, cold pressing, slitting and other processes are performed to obtain the negative electrode sheet; a PE porous polymer membrane treated with alumina ceramic is used as an isolation membrane; an electrolyte of 1 mol/L _LiPF6 solution is selected, and an organic solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) is prepared in a volume ratio of 5:2:3 and a film-forming additive is appropriately added to obtain the required electrolyte; the positive electrode sheet, the isolation membrane, and the negative electrode sheet are assembled in a dry room environment with a humidity of less than 2%, and then the corresponding electrolyte is filled and packaged after baking and drying, and a soft-pack battery with a capacity of 2.8Ah is prepared through a formation test, and an electrical performance test is performed.

Embodiment 2:

Cathode slurry preparation:

The positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , the binder PVDF, and the conductive agent carbon black were mixed in a ratio of 90:5:5, and the corresponding ammonium fluoride was added according to the residual lithium content. After dry mixing for 15 minutes, NMP was added and stirred at a high speed of 1000 rpm for 120 minutes, and then the bubbles were removed and the gas was exhausted to finally obtain a uniform positive electrode slurry with a solid content of 70%;

Positive electrode preparation

The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and the oven temperature is set to 130°C to dry the electrode piece; then an aluminum fluoride protective film and a lithium fluoride protective film are deposited on the positive electrode piece using an atomic layer deposition device, wherein the aluminum fluoride film precursor A is ground _TiF4 , the precursor B is _AlCl3 , the lithium fluoride film precursor A is lithium tert-butoxide, the precursor B is _TiF4 , and the deposition temperature is 250°C. The positive electrode sheet is placed in the atomic layer deposition ALD reaction chamber, and the deposition parameters and deposition process of the aluminum fluoride composite film are as follows: 1) evacuate the reaction chamber and wait until the pressure drops below 10Pa; 2) open the valve of precursor A, put _AlCl3 vapor into the reaction chamber, and maintain it for 15 seconds, and the temperature of the generated vapor is 120°C; 3) introduce argon gas into the reaction chamber for 120 seconds, then open the vacuum and take away the unreacted precursor A; 4) wait until the pressure in the reaction chamber drops to 10Pa, open the valve of precursor B, put _TiF4 into the reaction chamber, and maintain it for 15 seconds, and the temperature of the generated vapor is 120°C; 5) introduce argon gas into the reaction chamber for 120 seconds, then open the vacuum and take away the unreacted precursor B; from 1) to 5) is a complete aluminum fluoride deposition cycle. The deposition parameters and deposition process of lithium fluoride composite film are as follows: 1) evacuate the reaction chamber until the pressure drops below 10Pa; 2) open the valve of precursor A, introduce lithium tert-butoxide vapor into the reaction chamber, and maintain for 15 seconds, the temperature of the generated vapor is 165°C; 3) introduce argon gas into the reaction chamber for 120 seconds, then open the vacuum to take away the unreacted precursor A; 4) wait for the pressure in the reaction chamber to drop to 10Pa, open the valve of precursor B, introduce TiF ₄ vapor into the reaction chamber, and maintain for 15 seconds, the temperature of the generated vapor is 120°C; 5) introduce argon gas into the reaction chamber for 120 seconds, then open the vacuum to take away the unreacted precursor B; 1)-5) is a complete lithium fluoride deposition cycle. A protective film with a thickness of about 10nm is obtained by alternating the deposition of LiF and AlF ₃ in a 1:1 ratio; the electrode piece treated with the protective film is subjected to cold pressing, slitting and other processes to obtain an assembled positive electrode piece.

Preparation of battery components and finished products is the same as in implementation 1

Embodiment 3:

On the basis of Example 2, the number of deposition cycles was adjusted to obtain a protective film with a thickness of 20 nm.

Example 4

The positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , the binder PVDF and the conductive agent carbon black were dry mixed at a ratio of 90:5:5 for 15 minutes, and NMP was added and stirred at a high speed of 1000 rpm for 120 minutes to remove bubbles, and finally a uniform positive electrode slurry with a solid content of 70% was obtained.

(2) Preparation of positive electrode sheet is the same as in Example 2

(3) Preparation of battery components and finished products is the same as in Implementation 1

Example 5-Example 9

On the basis of Example 1, the number of deposition cycles was adjusted to obtain protective films of different thicknesses.

Comparative Example 1

(1) Preparation of positive electrode slurry:

The positive electrode material LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , the binder PVDF and the conductive agent carbon black were dry mixed at a ratio of 90:5:5 for 15 minutes, and NMP was added and stirred at a high speed of 1000 rpm for 120 minutes to remove bubbles, and finally a uniform positive electrode slurry with a solid content of 70% was obtained.

(2) Preparation of positive electrode

The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil and dried.

(3) Preparation of battery components and finished products is the same as in Implementation 1

Comparative Example 2

Cathode slurry preparation

The preparation method of the positive electrode slurry is the same as that in Example 1.

(2) Preparation of positive electrode

The positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil and dried.

(3) Preparation of battery components and finished products is the same as in Implementation 1

The prepared battery was tested using the following method:

1. Slurry static test:

The prepared positive electrode slurry was placed in an environment with a temperature of 25° C. and a humidity of 40% for 24 h, and the surface state of the positive electrode slurry was observed.

2. Capacity test

The charge and discharge test was carried out at a temperature of 25°C using a voltage range of 0.33C/0.33C 2.8-4.25V, and the discharge capacity was recorded.

3. Gas production test

The fully charged lithium-ion battery was placed in a 70°C constant temperature box. After 30 days, its volume was measured by the discharge method and converted into mL/Ah.

4. Cycle test

The charge and discharge test was carried out for 300 cycles at a temperature of 45°C in the 1C/1C 2.8-4.25V voltage range, and the capacity retention rate was recorded.

Table 1 Experimental data list

It can be seen from the above table that: the present application can effectively improve the gel condition of the slurry by adding additives to remove residual lithium when stirring the positive electrode material, and can effectively improve the specific capacity of the battery through the protective film, reduce the high-temperature gas production level, and improve the high-temperature cycle life of the battery. This is because while the composite protective film purifies the residual lithium, its product and the composite protective film have ion transmission properties, thereby improving the ion transmission performance of the surface of the positive electrode material. At the same time, the protective film can effectively protect the surface of the positive electrode material under high-temperature degradation conditions, inhibit the oxidation and side reaction process of the active substance to the electrolyte, maintain the structural stability and surface stability of the positive electrode material, and significantly improve the cycle life and gas production level of the battery.

The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent structural changes made using the contents of the present invention's specification and drawings, or directly/indirectly applied in other related technical fields, are included in the patent protection scope of the present invention.

Claims (25)

1. The positive pole piece is characterized by comprising a current collector and a coating arranged on at least one side of the current collector, wherein a protective film is arranged on the surface of the coating, and the protective film is made of fluoride.

2. The positive electrode sheet according to claim 1, wherein the thickness of the protective film ranges from 1nm to 50nm, preferably from 5nm to 20nm.

3. The positive electrode sheet according to claim 1 or 2, wherein the fluoride comprises at least one of lithium fluoride and aluminum fluoride.

4. The positive electrode sheet according to any one of claims 1 to 3, wherein the protective film comprises a lithium fluoride protective film and an aluminum fluoride protective film, the lithium fluoride protective film and the aluminum fluoride protective film being laminated on a surface of the coating layer;

and/or the protective film comprises a lithium fluoride protective film and an aluminum fluoride protective film, wherein at least part of the surface of the coating is provided with the lithium fluoride protective film, and at least the other part of the surface of the coating is provided with the aluminum fluoride protective film.

5. The positive electrode sheet according to any one of claims 1 to 4, wherein the coating layer includes a positive electrode material, and a coating layer including at least one of a sulfur-containing compound, a boron-containing compound, and a fluoride is formed on a surface of the positive electrode material.

6. The positive electrode sheet of claim 5, wherein the coating layer is lithium fluoride.

7. The positive electrode sheet according to claim 6, wherein the mass of the lithium fluoride is 0.01 to 5%, preferably 0.5 to 1.2% by mass of the total mass of the positive electrode material.

8. The positive electrode sheet according to any one of claims 1 to 7, wherein the positive electrode material in the coating layer has a general formula of Li _xNi_yM_1-yO₂, x is 0.9-1.15,0.6-y is 1, and m is one or more selected from Co, mn, and Al;

And/or the general formula of the positive electrode material in the coating is xLi ₂MnO₃.(1-x)LiMO₂, x is more than or equal to 0.1 and less than or equal to 0.9, and M is selected from one or more of Co, mn and Al.

9. A method of producing the positive electrode sheet according to any one of claims 1 to 8, comprising:

Preparing a positive electrode plate;

Preparing a precursor of fluoride;

And forming a protective film on the surface of the coating of the positive electrode plate by a film deposition technology.

10. The method of claim 9, wherein the thin film deposition technique comprises an atomic layer deposition process.

11. The method of producing a positive electrode sheet according to claim 9 or 10, wherein the fluoride comprises lithium fluoride and/or aluminum fluoride.

12. The method for manufacturing a positive electrode sheet according to claim 10 or 11, wherein in the step of forming a coating layer on the coated surface of the positive electrode sheet by an atomic layer deposition process, comprising:

Placing the positive electrode plate into an atomic layer deposition reaction chamber, vacuumizing, and setting the deposition temperature to be 200-250 ℃;

And (3) introducing a proper fluoride precursor into the reaction chamber, forming a protective film on the surface of the coating, opening vacuum to remove unreacted precursor, and repeating the steps to obtain the protective film with the preset thickness.

13. The method for preparing a positive electrode sheet according to claim 12, wherein a protective film is formed on the surface of the coating layer by introducing a precursor of a proper fluoride into the reaction chamber, vacuum is opened to remove unreacted precursor, and the above steps are repeated to obtain a protective film of a predetermined thickness, comprising:

introducing a precursor of aluminum fluoride into the reaction chamber, forming a protective film on the surface of the coating, and opening vacuum to remove unreacted precursor;

introducing a precursor of lithium fluoride into the reaction chamber, forming a protective film on the surface of the coating, and opening vacuum to remove unreacted precursor;

Repeating the steps to obtain the protective film with the preset thickness.

14. The method of manufacturing a positive electrode sheet according to claim 13, wherein the step of introducing a precursor of aluminum fluoride into the reaction chamber to form a protective film on the surface of the coating layer, and opening a vacuum to remove unreacted precursor comprises:

Vacuumizing the reaction chamber, and reducing the pressure to 10Pa or below;

AlCl ₃ gas is put into the reaction chamber, and the reaction time is maintained for 10s-20s;

Introducing purge gas into the reaction chamber, and opening vacuum to take away unreacted AlCl ₃ gas;

Reducing the pressure in the reaction chamber to 10Pa or below, and putting TiF ₄ gas into the reaction chamber for 10s-20s;

Introducing purge gas into the reaction chamber, and opening vacuum to take away unreacted TiF ₄ gas;

repeating the steps to obtain the aluminum fluoride protective film with the preset thickness.

15. The method for preparing a positive electrode sheet according to claim 13 or 14, wherein the step of introducing a precursor of lithium fluoride into the reaction chamber to form a protective film on the surface of the coating layer and opening a vacuum to remove unreacted precursor comprises:

Vacuumizing the reaction chamber, and reducing the pressure to 10Pa or below;

introducing alkyl lithium vapor into the reaction chamber, and maintaining for 10s-20s;

Introducing purge gas into the reaction chamber, and opening vacuum to take away unreacted alkyl lithium vapor;

reducing the pressure in the reaction chamber to 10Pa or below, and introducing TiF ₄ vapor into the reaction chamber for 10s-20s;

Introducing purge gas into the reaction chamber, and opening vacuum to take away unreacted TiF ₄ vapor;

Repeating the steps to obtain the lithium fluoride protective film with the preset thickness.

16. The method for producing a positive electrode sheet according to any one of claims 9 to 15, characterized in that in the step of preparing a positive electrode sheet, it comprises:

Mixing and reacting a positive electrode material with a reactive substance, wherein a coating layer is formed on the surface of the positive electrode material;

mixing the anode material with the coating layer, a binder and a conductive agent, adding a solvent, and stirring to obtain anode slurry;

Coating the positive electrode slurry on a current collector, and drying to obtain a positive electrode plate;

Wherein the reactive material comprises at least one of a sulfur compound and a boron compound.

17. The method for producing a positive electrode sheet according to any one of claims 9 to 15, characterized in that in the step of preparing a positive electrode sheet, it comprises:

Mixing a positive electrode material, a binder, a conductive agent and ammonium fluoride, adding a solvent, and stirring to obtain positive electrode slurry;

and coating the positive electrode slurry on a current collector, and drying to obtain a positive electrode plate.

18. The method for preparing a positive electrode sheet according to claim 17, wherein the ammonium fluoride is added in an amount ranging from 0.009% to 4.5%, preferably from 0.45% to 1.1% by mass of the positive electrode material.

19. The method according to any one of claims 17 and 18, wherein the step of mixing the positive electrode material, the binder, the conductive agent, and the ammonium fluoride, adding the solvent, and stirring to obtain the positive electrode slurry comprises:

mixing the positive electrode material, the binder, the conductive agent and the ammonium fluoride for 5-60 min, adding a solvent, stirring for 30-3 h at the rotating speed of 300-2000 r/min, removing bubbles, and exhausting air to obtain the positive electrode slurry with the solid content of 60-85%.

20. The method of producing a positive electrode sheet according to any one of claims 17 to 19, wherein in the step of coating the positive electrode slurry on a current collector and drying to obtain a positive electrode sheet, comprising:

And (3) coating the positive electrode slurry on a current collector, and drying at the temperature of 100-170 ℃ to obtain a positive electrode plate.

21. The method for producing a positive electrode sheet according to any one of claims 16 to 20, wherein a ratio of a residual lithium mass in the positive electrode material to the positive electrode material mass is equal to or more than 0.02% Li ₂CO₃ and equal to or more than 0.2% LiOH.

22. An electrode assembly comprising the positive electrode sheet according to any one of claims 1 to 8, or comprising the positive electrode sheet produced by the positive electrode sheet production method according to any one of claims 9 to 21.

23. A battery cell is characterized in that, the battery cell comprising the electrode assembly of claim 22.

24. A battery, characterized in that, the battery comprising the battery cell of claim 23.

25. An electric device is characterized in that, the power utilization device comprises the battery cell of claim 23 or the battery of claim 24.